Trajectory data compression

ABSTRACT

A method, computer system, and computer readable product for trajectory data compression are disclosed. In embodiments, the method comprises generating spatial data for one or more moving objects; projecting the data onto a network comprised of a plurality of trajectories, the network constraining movement of the one or more moving objects; and storing the projected data in a data store. In embodiments of the invention, the method further comprises translating updates and queries to the spatial data, using specified data of the network, into links to the data store, and using the links to update and query the data store. In embodiments of the invention, the specified data of the network are stored in a network store. In embodiments of the invention, each of the trajectories includes one or more sub-trajectories, and the projecting the spatial data onto a network includes projecting the spatial data onto the sub-trajectories.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Contract No.:W911NF-09-2-0053 awarded by the Army Research Office (ARO). TheGovernment has certain rights in this invention.

BACKGROUND

This invention generally relates to compressing spatiotemporal data.

Large volumes of spatiotemporal data are being generated by movingobjects (e.g., the connected cars initiative). A key challenge with thisdata is to simultaneously support: (i) high spatial update rates tohandle moving objects, and (ii) high query rates to answer spatialqueries (e.g., when an accident happens, notify nearby cars). In orderto sustain high query rates, traditional solutions index inputs (andupdates) using a spatial index (e.g., DB2 grid index, Informix r-treeindex, etc.).

The rate at which a database can support updates depends on the natureof indexing; generally a no-index update is faster than a hash mapupdate (equality query) followed by a b-tree index update (for rangequeries) followed by a r-tree/grid index update (for spatial queries).The rate of updates (even today and more so in the near projectedfuture) is above the rate at which commercial databases can handlespatial updates (i.e., insert and update spatial index).

SUMMARY

Embodiments of the invention provide a method, computer system andcomputer readable product for trajectory data compression. Inembodiments, the method comprises generating spatial data for one ormore moving objects; projecting the spatial data onto a networkcomprised of a plurality of defined trajectories, the networkconstraining movement of the one or more moving objects; and storing theprojected spatial data in a spatial data store.

In embodiments of the invention, the method further comprisestranslating updates and queries to the spatial data, using specifieddata of the network, into links to the spatial data store, and usingsaid links to update and query the spatial data store.

In embodiments of the invention, the method further comprises storingthe specified data of the network in a network store.

In embodiments of the invention, each of the defined trajectoriesincludes one or more sub-trajectories, and the projecting the spatialdata onto a network includes projecting the spatial data onto thesub-trajectories.

In embodiments of the invention, the moving objects move along thesub-trajectories of the network; and the projecting the spatial dataonto the sub-trajectories includes generating one or more data sets foreach of the moving objects, each of the data sets including a valuerepresenting one of the sub-trajectories along which said each movingobject moves.

In embodiments of the invention, each of the data sets for each of themoving objects further includes one or more time values associated withsaid each moving object and said one of the sub-trajectories along whichsaid each moving object moves.

In embodiments of the invention, said one or more time values includes atime value indicating when said each moving object starts moving alongsaid one of the sub-trajectories.

In embodiments of the invention, said one or more time values includes atime value indicating when said each moving object ends moving alongsaid one of the sub-trajectories.

In embodiments of the invention, each of the data sets for each of themoving objects further includes a spatial value identifying a locationof the each moving object along said one of the sub-trajectories.

In embodiments of the invention, each of the sub-trajectories includes aplurality of sample points; and the generating one or more data sets foreach of the moving objects includes generating, for said each movingobject, one of the data sets at each of the sample points of said one ofthe sub-trajectories.

As discussed above, the rate at which a database can support updatesdepends on the nature of indexing; generally a no-index update is fasterthan a hash map update (equality query) followed by a b-tree indexupdate (for range queries) followed by a r-tree/grid index update (forspatial queries). The rate of updates (even today and more so in thenear projected future) is above the rate at which commercial databasescan handle spatial updates (i.e., insert and update spatial index). Inorder to address this challenge, new solutions are required tocompress/encode moving object data such that updates are faster, whileretaining high query rates.

In embodiments of the invention, updates and queries on spatial data aretranslated to that of updates and queries on hashmap indexed data and alarge but static (i.e., no updates—query only) spatial data.Effectively, large volumes of static spatial data are indexed (which canbe done offline)—and this index (S) is designed for high querythroughput. In the online mode, spatial updates and queries aretranslated using this static index S into simple hashmap index updatesand queries—which can sustain far higher rates than spatial indexupdates and queries.

While spatial data has large entropy, embodiments of the inventionproject the spatial data into a lower entropy space, namely, the roadnetwork which constrains the movement of most moving objects like cars,trucks, buses, etc. The road network can be treated as a large volume ofstatic spatial data that is indexed offline. In the online mode, aspatial update is mapped using the static spatial index into an opaque“linkId” (more generally, a poly-line/linestring which represents asub-trajectory) which then requires only a hashmap update (on thelinkId) for insertion. Similarly, a spatial query is mapped using thestatic spatial index into an opaque “linkId” which is then looked upusing the hashmap index—post processing is finally applied to selectexact matches to the spatial query.

An offline process is one that may be done at startup, or at regularintervals. It does not have any real-time-ness to it. For example,creating an index of the road network can be done as an offline processsince the underlying road network should not change often. An onlineprocess is one that is happening as the data are coming in. For example,as a vehicle is moving, its locations are being streamed to thetrajectory compression process, and compression is being performed in anonline manner.

Embodiments of the invention provide for compressing and indexingspatiotemporal data (data that has a location attribute in addition totimestamps) using a road network graph as a constraint.

Embodiments of the invention provide a method comprising translatingupdates and queries on spatial data to updates and queries on hash-mapindexed data and a large but static spatial data derived from a roadnetwork graph. This method can sustain far higher rates of spatial indexupdates and queries than what can be achieved with conventionalspatiotemporal data storage techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an architecture of a spatiotemporal data processingsystem incorporating embodiments of the invention.

FIG. 2 shows a table having time and position data for several vehiclesand three time series formed from that data.

FIG. 3 shows three images showing three vehicle trajectories andsub-track pattern models for those trajectories.

FIG. 4 is a table storing spatiotemporal data about a vehicle.

FIG. 5 shows a table that stores spatial data

FIG. 6 illustrates sub-trajectories of a trajectory and various pointsof interest along those sub-trajectories.

FIG. 7 illustrates a trajectory storage structure and procedure inaccordance with an embodiment of the invention.

FIG. 8 depicts a computing environment in which embodiments of theinvention may be implemented.

DETAILED DESCRIPTION

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Embodiments of the invention provide a method, system and computerreadable device for compressing spatiotemporal data. As discussed above,large volumes of spatiotemporal data are being generated by movingobjects, and a key challenge with this data is to support simultaneouslyhigh spatial update rates and high query rates to answer spatialqueries. In order to sustain high query rates, traditional solutionsindex inputs (and updates) using a spatial index. The rate of updatesneeded today by many spatiotemporal systems, however, is above the rateat which commercial databases can handle spatial updates.

This invention addresses this challenge. Generally, this is done bycompressing/encoding moving object data such that updates are fasterwhile retaining the ability to respond to high query rates.

FIG. 1 illustrates the architecture of a spatiotemporal data processingsystem 100. Generally, the architecture comprises analysis section 102,real time spatiotemporal store 104, pre-processing section 106, and datastore 110.

Three types of data are saved in data store 110, time series data 112,spatial data 114, and road network data 116. Analysis section 102includes the functions used to analyze the data in the data store. Thesefunctions include a trajectory similarity analysis 120, trajectorypattern mining 122, activity recognition on trajectory 124, andperiodical pattern mining 126. Other data analysis functions may also beprovided.

Real time spatiotemporal store 104 includes trajectory indexing 130,trajectory point query 132, trajectory range query 134, spatiotemporaldata store (time series) 136, and spatiotemporal data store (spatial)140.

The pre-processing section 106 provides a number of functions forpre-processing spatiotemporal data, for example, before the data arestored in one of the data stores or processed by one of the otherfunctions provided by architecture 100. In the embodiment shown in FIG.1, pre-processing 106 includes trajectory compression 142, an outlierfilter 144, staying detection 146, map matching 150, route patternmining 152, and road network building 154.

In embodiments of the invention, architecture 100, and specifically,pre-processing 106, receives input data. For example, the input data mayinclude moving object data, which may be, for instance, globalpositioning satellite data. Other input data may include road statusdata.

As discussed above, very large volumes of spatiotemporal data are beinggenerated by moving objects. For example, 100,000 to 1,000,000 carsgenerating data at a rate of 1,000 plus data points per second, willgenerate approximately 100 TB of data per year. This huge volume of datapresents challenges: real time persistence of data from approximately100,000 to 1,000,000 vehicles connected into the internet of thingsCloud with efficient data store/index to support spatial temporal query,especially for trajectory query.

FIG. 2 shows a table 200 having time and position data for threevehicles, represented at 202, 204 and 206, and a time series 210, 212and 214 for each of these vehicles formed from this data. In particular,for each of these vehicles, the table 200 includes a number of timevalues, the location of the vehicle at that time, and a CAN value forthat location. For instance, the table shows that at time 00:00 vehicle202 is at location 1,1, vehicle 204 is at location 6,11, and vehicle 206is at location 9,4. At time 02:31, vehicle 204 is at location 3,12 andvehicle 206 is at location 11,5; and at time 10:35, vehicles 202 and 204are both at location 2,2, and vehicle 206 is at location 15,8.

The group of time series 210, 212, 214 is formed from this data. Eachtime series includes a plurality of data sets for one of the vehiclesarranged in order of time. Each data set, in turn, includes a time andthe position of the vehicle at that time.

These time series representations provide for a compact, efficientstorage for an unlimited number of time-indexed observations (locations,CAN, etc.) for each vehicle. This time series representation makesqueries of the type “where was X at this time” easy to answer. Anexample of such a query is: Find out all the trajectory records ofpublic bus 12345 yesterday.

Other queries, though, may be difficult to answer using these timeseries representations. For instance, the query: “When was X around agiven region” may be hard to answer with this time seriesrepresentations. Extensive scanning of raw data may be needed to answersome types of queries when the data are stored in these time seriesrepresentations.

Embodiments of the invention provide the ability to search deeply intorealtime spatiotemporal data, and embodiments of the invention functionas real time spatial temporal historian. Achieving this presentschallenges.

One of these challenges is spatial data inserts. To address thischallenge, in embodiments of the invention, a continuous trajectory ispartitioned into a list of small sub-trajectories, or sub-tracks, andthe data for these sub-tracks are inserted as Line_String values with RTree index but with significant redundancy and index updates. Forexample, updates may be at a rate of 1 k/second.

FIG. 3 shows three trajectories 302, 304, 306 partitioned into subtracks. Trajectory 302 includes sub-tracks 302 a and 302 b, trajectory304 includes sub-tracks 304 a, 304 b and 304 c, and trajectory 306includes sub-tracks 306 a, 306 b and 3206 c. FIG. 3, in addition, givesthe start and end times for each of these trajectories.

Embodiments of the invention store the sub-track data in a node networkmodel (by real time map matching) so as to offload the extensivedirectly updating of track data to the R-tree. Also, together with timeseries, embodiments of the invention provide redundant sub-track codestorage for fast response to typical trajectory queries (Point,Partition, and Join queries) in on-line transaction processing (OLTP)mode.

Queries for which a fast response may be available include, for example:“Find out the most frequently passed gas stations by my fleet in year2012” (for identifying contract gas stations); and “Find out the taxithat passed through this specific point of interest (POI) yesterdaybetween 9:00-9:20” (for handling item lost claims). Embodiments of theinvention can provide fast responses to other types of queries.

Embodiments of the invention provide a spatiotemporal store and querybased on a network model. The store and query operations use time seriesto store spatial and temporal data for moving objects, storesub-trajectory data as a linked list in the road network, and use UDRfor spatiotemporal query of moving objects.

FIGS. 4 and 5 show two tables that may be used in embodiments of theinvention. FIG. 4 shows a table 400 of output from pre-processing 106 ofFIG. 1 to time series store 110, and FIG. 5 shows a table 500 of outputfrom this pre-processing to spatial store.

More specifically, the table 400 of FIG. 4 shows time series data for aparticular moving object. With the example shown in FIG. 4, this dataincludes the identity (modid) of the moving object, a time or timestamp,the position (point x,y) of the moving object at that time, a flag toindicate whether this data are a new start (a new trip for the movingobject), and other properties of the sampling point.

The table 500 of FIG. 5 shows spatial data. As shown in the FIG. 5, thistable includes the identity (modid) of the moving object, the start timeat which the object enters a particular sub-trajectory, the time atwhich the object leaves that sub-track, and the first position, referredto as the anchor point, of the object on that sub-trajectory. The tablealso includes a flag to indicate the status of that anchor point. Asdiscussed in more detail below, there are four types of status, referredto as starting, staying, junction, and unknown.

In embodiments of the invention, the table of FIG. 5 also includes alink or summary id, which is the link or summary that the trajectory ismapped to in this interval. The summary can be obtained by route patternmining. In addition, this table includes the average speed of the objectin this interval.

FIG. 6 illustrates two sub-trajectories 602, 604 and a number ofpre-specified points on those sub-trajectories. There are fourcategories for the points: sample points 606, staying points 610,junction points 612 and starting points 614. Individual points may be inmore than one category. All the pre-specified points are considered assample points, and starting points are the points on a sub-trajectory atwhich the moving object starts on that sub-trajectory. Staying pointsare the points on a sub-trajectory to which the moving object moveswhile staying on the sub-trajectory, and junction points are the pointsat the junction of two sub-trajectories.

In embodiments of the invention, there are data requirements forpreprocesses in streams. For a timeseries store using the timeseriestable, pre-process requirements include filtering/adjusting outliersusing a matched route, finding starting points among raw points, andcompressing raw data. This compression should guarantee correction oflinear interoperation (less than deviation) when uncompressing. Thepre-process requirements also include inserting junction points amongraw points. Embodiments of the invention estimate timestamps for thejunction points.

The data to be stored includes raw points with starting flag aftercompression and junction points.

Also, time values are inserted. When a sample point goes topre-processing, there can be three kinds of outputs: (1) no output: thesampling point is filtered out or compressed; (2) output the inputsample point; and (3) output two points (the first point is the junctionpoint, and the second point is the sample point. If the sampling pointis a junction point, just the input sample point is output.). Batchinsert can be used.

For spatial store using linkid, pre-process requirements includeidentifying point status (starting point, staying point, junction point,etc.) and matching to linkid. The pre-process requirements also includeprocessing summary linkid for proper situation. The data to be storedincludes records for status changes. In addition, time values areinserted. For example, when a new status is entered, the previous statusis recorded to the sub-track table. Batch insert can be used.Embodiments of the invention may use time outs when there is no newstatus or no GPS reporting for a specified time.

FIG. 7 illustrates trajectory storage structure 700 using linkid. InFIG. 7, a trajectory of a moving object is shown at 702. This trajectoryis comprised of a series of sub-trajectories including sub-trajectories702 a, 702 b and 702 c. Map-matching is used to map thesesub-trajectories to a Linkid store 704 for sub-tracks. Given x,ycoordinates identify the sub-tracks. Redundant storage 706 is providedby storing two-dimensional point data in time series store.

Data in store 704 may be accessed by Rtree-indexing represented at 710,and road edges indexing can also be done. The data in store 704 providesspatiotemporal query capability, represented at 712. Query UDR is alsosupported.

A trajectory storage schema 720 is also represented in FIG. 7. Thisstorage schema provides a table 722 for each vehicle (T_Vehicle) and atable 724 for each subtrack (T_Subtrack). For each vehicle, the table722 stores the vehicle id (modid(PK)), and a time series (ts_track). Forthis time series, a row is created; and values including a timestamp,datetime, year data, x and y position values, and a flag, are stored.Other information, such as the vehicle type, color and owner, may alsobe stored in the table in user defined columns.

Each sub-track table 724 stores a vehicle id (modid(FK)), the start timeof the vehicle on the sub-track, the end time of the vehicle on thesub-track, and the starting point of the vehicle on the sub-track. Thetable 724 may also store a flag, a linkid, and the speed of the vehicleon the track.

In this trajectory storage schema 720, Rowtype (r_track) and Table(T_Vehicle) are defined by a user. Tables (T_subtrack, T_Edge,T_Junction) are defined by historian system. Trajectory is stored inTimeseries: a sequence of tuples (timestamp, (x,y), flag).

Embodiments of the invention provide real time persistence of 3V movingobject data for efficient historical typical trajectory oriented query,including point query, range query, and join query.

Point queries are related to a single trajectory. These include queriessuch as “Where was X at this time?” To answer such a query, a timeseriesquery function is reused directly to get row data (trajectory) accordingto a time range. Point queries also include queries such as “When was Xat this location?” Other types of point queries include, for instance,trajectory retrieve queries, and queries about a relationship withregion R within distance d. For example, a query may be for an object idwithin distance d from region R between a start time and an end time(the object is considered to “cross” the region). Other queries may befor an object id within distance d from region R always between a starttime and an end time (the object is considered to be “within” theregion), and a query for an object id that stays in region R for atleast an interval of time between a start time and an end time (theobject is considered as “staying” in the region).

Another type of point query involves a number of points of interest(POI). For example, a query may be, from many points of interest, findthe ones which satisfy the spatiotemporal relationship to the trajectory(KNN-POI). A query of this type may be used, for instance, to find theclosest gas station to this trajectory between a start time and an endtime.

Range queries retrieve trajectories that stand in certain relationshipsto a region. These include queries of the type where a specifiedcondition is satisfied by the objects that stand in certainrelationships (e.g., within distance x) to a region R, during time T.Example range queries ask to find moving objects within distance d fromR sometime between a start time and an end time (the objects areconsidered to “cross” the region), and to find moving objects withindistance d from R always between a start time and an end time (theobjects are considered to be “within” R). Another example range query isto find moving objects that stay in R for at least a time intervalbetween start time and end time (the objects are considered as “staying”in the region).

Another type of range query asks for moving objects which satisfy thespatiotemporal relationship to a specified point or point. An exampleK-NN query would be: find the K nearest moving objects to region R at aspecific time.

Join queries are for identifying relationships between trajectories. Asan example, a join query asks for trajectories within a distancethreshold (i.e., pair distance of two trajectories). As another example,a join query asks for spatiotemporal regions which are frequently passedby a set of trajectories (frequent pattern mining).

As will be apparent to those of ordinary skill in the art, any suitableprocessors, computers and servers may be used in embodiments of theinvention, and FIG. 8 illustrates a computer system 800 in whichembodiments of the present disclosure, or portions thereof, may beimplemented. A processor unit or device as discussed herein may be asingle processor, a plurality of processors, or combinations thereof.Processor devices may have one or more processor “cores.” The terms“computer program medium,” “non-transitory computer readable medium,”and “computer usable medium” as discussed herein are used to generallyrefer to tangible media such as a removable storage unit, and a harddisk installed in a hard disk drive.

Processor device 804 may be a special purpose or a general purposeprocessor device. The processor device 804 may be connected to acommunications infrastructure 806, such as a bus, message queue,network, multi-core message-passing scheme, etc. The network may be anysuitable network and may include a local area network (LAN), a wide areanetwork (WAN), a wireless network (e.g., WiFi), a mobile communicationnetwork, a satellite network, the Internet, fiber optic, coaxial cable,infrared, radio frequency (RF), or any combination thereof. Othersuitable network types and configurations will be apparent to personshaving skill in the relevant art. The computer system 800 may alsoinclude a main memory 808 (e.g., random access memory, read-only memory,etc.), and may also include a secondary memory 810. The secondary memory810 may include the hard disk drive 812 and a removable storage drive814, such as a floppy disk drive, a magnetic tape drive, an optical diskdrive, a flash memory, etc.

The removable storage drive 814 may read from and/or write to theremovable storage unit 418 in a well-known manner. The removable storageunit 418 may include a removable storage media that may be read by andwritten to by the removable storage drive 814. Data stored in thecomputer system 800 (e.g., in the main memory 808 and/or the secondarymemory 810) may be stored on any type of suitable computer readablemedia, such as optical storage (e.g., a compact disc, digital versatiledisc, Blu-ray disc, etc.) or magnetic tape storage (e.g., a hard diskdrive).

The computer system 800 may also include a communications interface 824configured to allow software and data to be transferred between thecomputer system 800 and external devices. Exemplary communicationsinterfaces 824 may include a modem, a network interface (e.g., anEthernet card), a communications port, a PCMCIA slot and card, etc.

Computer program medium and computer usable medium may refer tomemories, such as the main memory 808 and secondary memory 810, whichmay be memory semiconductors (e.g., DRAMs, etc.). These computer programproducts may be means for providing software to the computer system 800.Computer programs (e.g., computer control logic) may be stored in themain memory 808 and/or the secondary memory 810.

Those of ordinary skill in the art will appreciate that the hardwaredepicted in FIG. 8 may vary. The depicted example is not meant to implyarchitectural limitations with respect to the present invention.

The description of the invention has been presented for purposes ofillustration and description, and is not intended to be exhaustive or tolimit the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope of the invention. The embodiments werechosen and described in order to explain the principles and applicationsof the invention, and to enable others of ordinary skill in the art tounderstand the invention. The invention may be implemented in variousembodiments with various modifications as are suited to a particularcontemplated use.

The invention claimed is:
 1. A computer-implemented method of trajectorydata compression comprising: generating, in a computer processor system,spatial data for one or more moving objects; projecting, by the computerprocessor system, the spatial data onto a network comprised of aplurality of defined trajectories, the network constraining movement ofthe one or more moving objects to the defined trajectories; storing, bythe computer processor system, the projected spatial data in a spatialdata store, including generating one or more data sets for each of themoving objects, each of the data sets including a value representing oneof the trajectories on which said each moving object moves, and a linkto said one of the trajectories; and mapping spatial updates and spatialqueries, using a static spatial index, into links representing thetrajectories and using the links to update and query the spatial datastore.
 2. The method according to claim 1, further comprising:translating updates and queries to the spatial data, using specifieddata of the network, into links to the spatial data store, and usingsaid links to update and query the spatial data store.
 3. The methodaccording to claim 2, further comprising storing the specified data ofthe network in a network store.
 4. The method according to claim 2,wherein: each of the defined trajectories includes one or moresub-trajectories; and the projecting the spatial data onto a networkincludes projecting the spatial data onto the sub-trajectories.
 5. Themethod according to claim 4, wherein: the moving objects move along thesub-trajectories of the network; and the projecting the spatial dataonto the sub-trajectories includes generating one or more data sets foreach of the moving objects, each of the data sets including a valuerepresenting one of the sub-trajectories along which said each movingobject moves.
 6. The method according to claim 5, wherein each of thedata sets for each of the moving objects further includes one or moretime values associated with said each moving object and said one of thesub-trajectories along which said each moving object moves.
 7. Themethod according to claim 6, wherein said one or more time valuesincludes a time value indicating when said each moving object startsmoving along said one of the sub-trajectories.
 8. The method accordingto claim 6, wherein said one or more time values includes a time valueindicating when said each moving object ends moving along said one ofthe sub-trajectories.
 9. The method according to claim 5, wherein eachof the data sets for each of the moving objects further includes aspatial value identifying a location of the each moving object alongsaid one of the sub-trajectories.
 10. The method according to claim 5,wherein: each of the sub-trajectories includes a plurality of samplepoints; and the generating one or more data sets for each of the movingobjects includes generating, for said each moving object, one of thedata sets at each of the sample points of said one of thesub-trajectories.
 11. A computer system for trajectory data compressioncomprising: a storage device storing program code: and one or moreprocessor units connected to the storage device for executing theprogram code for: receiving spatial data for one or more moving objects;projecting the spatial data onto a network comprised of a plurality ofdefined trajectories, the network constraining movement of the one ormore moving objects, to the defined trajectories; storing the projectedspatial data in a spatial data store, including generating one or moredata sets for each of the moving objects, each of the data setsincluding a value representing one of the trajectories on which saideach moving object moves, and a link to said one of the trajectories;and mapping spatial updates and spatial queries, using a static spatialindex, into links representing the trajectories and using the links toupdate and query the spatial data store.
 12. The computer systemaccording to claim 11, wherein the one or more processing unit furtherexecute the program code for: translating updates and queries to thespatial data, using specified data of the network, into links to thespatial data store, and using said links to update and query the spatialdata store.
 13. The computer system according to claim 12, wherein theone or more processing unit further execute the program code for storingthe specified data of the network in a network store.
 14. The computersystem according to claim 12, wherein: each of the defined trajectoriesincludes one or more sub-trajectories; and the projecting the spatialdata onto a network includes projecting the spatial data onto thesub-trajectories.
 15. The computer system according to claim 14,wherein: the moving objects move along the sub-trajectories of thenetwork; and the projecting the spatial data onto the sub-trajectoriesincludes generating one or more data sets for each of the movingobjects, each of the data sets including a value representing one of thesub-trajectories along which said each moving object moves.
 16. Acomputer program product comprising: a computer readable storage mediumhaving computer program code tangibly embodied therein for trajectorydata compression, the computer program code, when executed in a computersystem, performing the following: receiving spatial data for one or moremoving objects; projecting the spatial data onto a network comprised ofa plurality of defined trajectories, the network constraining movementof the one or more moving objects to the defined trajectories; storingthe projected spatial data in a spatial data store, including generatingone or more data sets for each of the moving objects, each of the datasets including a value representing one of the trajectories on whichsaid each moving object moves, and a link to said one of thetrajectories; and mapping spatial updates and spatial queries, using astatic spatial index, into links representing the trajectories and usingthe links to update and query the spatial data store.
 17. The computerprogram product according to claim 16, wherein the computer programcode, when executed in the computer system, further performs thefollowing: translating updates and queries to the spatial data, usingspecified data of the network, into links to the spatial data store, andusing said links to update and query the spatial data store.
 18. Thecomputer program product according to claim 17, wherein the computerprogram code, when executed in the computer system, further performs thefollowing: storing the specified data of the network in a network store.19. The computer program product according to claim 17, wherein: each ofthe defined trajectories includes one or more sub-trajectories; and theprojecting the spatial data onto a network includes projecting thespatial data onto the sub-trajectories.
 20. The computer program productaccording to claim 19, wherein: the moving objects move along thesub-trajectories of the network; and the projecting the spatial dataonto the sub-trajectories includes generating one or more data sets foreach of the moving objects, each of the data sets including a valuerepresenting one of the sub-trajectories along which said each movingobject moves.